1. Field of the Invention
The present invention is directed to a new class of fluorinated aryl acetylenes useful as monomers in the polymerization of a low dielectric constant polymer which has excellent thermal stability. In addition, the present invention is directed to a polymeric reaction product of the new class of fluorinated aryl acetylenes, a diphenyloxide biscyclopentadienone and, optionally, 1,3,5-tris(phenylacetylene)benzene.
2. Background of the Prior Art
The continuing decrease in the size of integrated circuits has resulted in the development of dramatically decreased size integrated circuits wherein the spaces between individual devices or elements thereon are similarly diminished. This development has put increased insulative demand upon insulators, disposed between conductive paths, to prevent xe2x80x9ccross-talk,xe2x80x9d shorts and other integrated circuit failures. A limiting factor in the development of these devices has been the inability to insulate between decreased conductive paths which these insulative layers separate.
This problem has been addressed in the prior art by the development of fluorine silicate glass (FSG) films. However, these films, effective in the relatively large size integrated circuits of recent years, have proven inadequate insofar as the dielectric constant of these films has proven to be too high to prevent xe2x80x9ccross talk,xe2x80x9d shorting and other manifestations of capacitance failure in the much smaller integrated circuits presently in use or under development. The insulating films currently employed in electrically insulating conductive layers of integrated circuits, which are usually metallic layers, particularly copper layers, include little or no fluorine. The most recent of these new films are polyphenylenes, as exemplified by U.S. Pat. No. 5,965,679, which is incorporated herein by reference. These polyphenylene films, which are polymerized from a monomeric reaction product, are characterized by lower dielectric constants compared to films heretofore employed in this application.
Although these films represent a significant advance in the art, films having still further reduced dielectric constants are desired for the continued miniaturization of integrated circuits.
One such recent attempt is the attempt to modify a recently developed polyphenylene low dielectric constant film by adding fluorine thereto, based on the knowledge that fluorine-containing polymers have low dielectric constants, has proven unsuccessful. This is so in spite of the fact that the addition of a fluorine-containing co-monomer produces a polymeric product having reduced dielectric constant compared to equivalent polymers produced by prior art monomers which are free of fluorine.
The reason for this failure is that fluorinated polymeric films, which is the reaction product of monomers known in the prior art with an aliphatic fluorine-containing monomer, is that this film emits fluorine upon the application of heat. This fluorine reacts, especially in copper damascene structures, commonly utilized in present day integrated circuits, at the elevated temperatures at which integrated circuits operate, with tantalum to form volatile tantalum fluoride. This tantalum fluoride formation results in loss of adhesion between the insulating polymeric layer and the metal, e.g. copper, surface.
It is thus apparent that there is a significant need in the art for a fluorinated polymeric film having the same degree of thermal inertness characteristic of prior art FSG films but which has a significantly lower dielectric constant so that even thinner layers of that polymeric film may be employed in the effective insulation of conductive layers of present day integrated circuits.
The preparation of substituted aryl acetylenes is known in the art. Martin et al., xe2x80x9cSynthesis of Substituted Aryl Acetylenesxe2x80x9d, published August, 1991, exemplifies this teaching in the prior art.
Peters, Semiconductor Inter., 63-74 (September, 1998) provides a general background article describing the development of low dielectric constant materials for use in integrated circuits. This article evidences the concern in the art for improved low dielectric constant interlevel insulators.
U.S. Pat. No. 5,552,503 to Kwock et al. describes photodefinable dielectric layers comprising poly(aromatic diacetylenes). The poly(aromatic diacetylene) can be copolymerized with monomers, such as 4,4xe2x80x2-bis(3-ethynylphenoxy)octafluorobiphenyl, to produce a thermosetting polymer.
U.S. Pat. Nos. 5,827,907 and 5,834,537 to Gotra et al. both disclose thermosetting resins in which a thermoplastic polymer is dispersed. The thermosetting material may be an acetylene-terminated resin modified with a dultice fluorine-containing poly(arylene ether). The thermoplastic polymer is fluorine-containing.
U.S. Pat. No. 6,124,421 to Lau et al. sets forth poly(arylene ether) compositions which form dielectric layers. This disclosure provides a method for synthesizing bis(4-fluorophenyl)ethyne.
U.S. Pat. Nos. 5,965,679 and 6,288,188 disclose polyphenylene oligomers and polymers useful as dielectric resins in microelectronic fabrication. These polymers, which may be thermosetting, involve the reaction product of a biscyclopentadienone and a polyfunctional acetylene.
A new class of compounds useful as monomers in the formation of polymers which have lower dielectric constants than the polymeric films heretofore employed in electrically insulating conductive layers of integrated circuits has now been discovered. This new class of monomers is reacted with monomers employed in the prior art to polymerize polyphenylenes having lower dielectric constants than heretofore known in the art. These new monomers are characterized by the inclusion of fluorine substituents on ring carbon atoms to produce polymers which include fluorine. These polymers do not emit fluorine when subjected to temperatures to which films of low dielectric constant polymers, employed in integrated circuits, are usually exposed.
In accordance with the present invention a new class of fluorinated arylacetylene compounds has been developed which can be polymerized to produce a very low dielectric constant polymer useful in the fabrication of microelectronic devices. The arylacetylene compound within the scope of the present invention is selected from the group consisting of a compound having the structural formula 
where q and r are the same or different and are integers of 1 to 5; a compound having the structural formula 
where s and t are the same or different and are integers of 1 to 4; a compound having the structural formula 
where s and t have the meanings given above; a compound having the structural formula 
where u, v, w, x, y and z are the same or different and are integers of 1 to 4; and a compound having the structural formula 
where q, r, s and t have the meanings given above.
In further accordance with the present invention polymers having very low dielectric constant are provided. The polymers of the present invention are reaction products of the acetylene compounds of the present invention and a diphenyl oxide cyclopentadienyl compound having the structural formula 
where Ph is phenyl.